Powder coating techniques, of both the electrostatic and non-electrostatic types, are now extensively used in industry in connection with a wide diversity of workpieces. A persistent and virtually universal problem associated with such operations involves the effective handling of unused powder. This is especially true when coating occurs from fluidized bed or spraying operations, because there is a natural tendency for the particles of the powder, which tend to be of relatively fine mesh sizes, to drift beyond the area of coating. The results are the creation of annoyance and hazard to personnel present in the vicinity, and an increase in operating costs, due to waste of the coating material.
Accordingly, systems have been developed for controlling fugitive powder. They usually employ vacuum-operated collecting tanks, into which powder may be withdrawn from the coating area, to provide a reservoir from which recycle may be had. Some of these systems are very effective, and by-and-large are entirely satisfactory.
However, as will readily be appreciated, virgin powder must be introduced into the system to replenish that which has either been used in the coating operation, or has been depleted through unavoidable loss. Generally, it is necessary to shut down the powder recovery system to enable the fresh supply of powder to be introduced, which is both time-consuming and also inconvenient.
Furthermore, it will be appreciated that the makeup of powder taken from the coating operations will vary from that freshly supplied. This is due to the selective utilization of portions of the powder for coating, the tendency for the finer particles to escape from the system, etc. Nevertheless, if uniform coatings are to be obtained it is important that the composition of the powder be consistent throughout the period of operation. Adding a quantity of virgin powder to powder which has been recycled and collected will (if not otherwise mixed) result in distinct strata within the supply; coatings produced therewith will consequently vary.
Accordingly, it is the primary object of the present invention to provide a novel, vacuum-operated powder handling system which enables the introduction of fresh powder without curtailment or cessation of normal operations.
It is also an object of the invention to provide such a system wherein means is provided to ensure the uniformity of the blend of powder which is withdrawn therefrom.
Another object of the invention is to provide a system having the foregoing features and advantages, which is also of relatively simple and inexpensive construction, and which is efficient in operation and convenient in use.